Fluoroelastomers having excellent heat resistance, oil resistance, and chemical resistance have been used widely for sealing materials, containers and hoses.
Production of such fluoroelastomers by emulsion and solution polymerization methods is well known in the art; see for example U.S. Pat. Nos. 4,214,060 and 4,281,092. Generally, fluoroelastomers are produced in an emulsion polymerization process wherein a water-soluble polymerization initiator and a relatively large amount of surfactant are employed. The surfactant most often used for such processes has been ammonium perfluorooctanoate (C-8). Fluoroelastomers prepared in such processes leave the reactor in the form of a dispersion.
While C-8 works very well as a surfactant in the polymerization process, it is relatively expensive, and its future commercial availability is uncertain. Thus, it would be desirable to find other surfactants effective for use in the emulsion polymerization of fluoroelastomers.
U.S. Pat. No. 6,512,063 B2 discloses an emulsion polymerization process for the production of fluoroelastomers wherein a hydrocarbon sulfonate is employed as the dispersing agent. In this process, the surfactant is present in the reactor prior to initiation of the polymerization reaction. While the process works very well for a continuous process, the polymerization rate of a semi-batch polymerization is not suitable to sustain a commercially viable polymerization process.
It would be desirable to have a commercially attractive semi-batch emulsion polymerization process for fluoroelastomers wherein the surfactant employed is a hydrocarbon anionic surfactant rather than a fluorosurfactant.